explosions of shell fire, outgoing artillery fire, going into the suburbs around the center of the city, where i am. >> reporter: residents are caught in a worsening cross fire. >> people who came from areas that are being shelled, they are on the streets, many children, sometimes you see them crying, old people are sleeping on the ground. >> reporte but nothing is this horrific war has gotten the attention of u.s. officials more than this chemical weapons threat. >> these reports may mean that the united states and our allies are facing the prospect of an imminent use of weapons of mass destruction in syria. this may be the last warning we get. >> reporter: i can tell you planning for all sorts of con tin jen sips is already well under way. but military action would not be easy. it could take upwards of 75,000 troops to secure those chemical weapons, which no one is eager to provide. but president obama, diane, has warned that using those weapons is a red line. >> on the story for us tonight, martha raddatz, thank you, martha. >>> and now, we want to tell you about another turbulent ho